hrpE基因在水稻条斑病菌Hrp pilus形成和致病性中起重要作用

 水稻条斑病菌(Xanthomonas oryzae pv.oryzicola,Xooc)的hrp(hypersensitive response and pathogenicity)基因簇编码形成Ⅲ型分泌系统(T3SS),将致病性的效应分子通过HrpF转位装置注入水稻细胞中,从而导致水稻产生抗(感)病性,但Xooc的HrpE是否形成Hrp pilus还不清楚。本研究对Xooc的hrpE基因进行突变,发现hrpE突变体在水稻上丧失致病性和在烟草上丧失激发HR的能力。与水稻互作结果显示,hrpE突变体不能够与水稻细胞互作,其在水稻组织中的生长能力显著下降。电镜结果显示,hrpE突变体不能够形成Hrp pilus,从而导致水稻条斑病菌丧失在水稻上的致病性。功能互补结果显示,完整的hrpE基因可以恢复hrpE突变体在烟草上激发HR反应的能力、在水稻上的致病性以及在水稻薄壁细胞间形成Hrp pilus的能力,表明hrpE基因形成Hrp pilus是水稻条斑病菌分泌致病性效应分子的重要条件。

Key roles of hrpE gene of Xanthomonas oryzae pv. oryzicola in formation of Hrp pilus and pathogenicity in rice

The hrp(hypersensitive response and pathogenicity)genes of Xanthomonas oryzae pv. oryzicola (Xooc) encode a type Ⅲ secretion system (T3SS), through which T3SS effectors are injected into rice cells and resulting in susceptibility or resistance to the pathogen infection. However, it is unclear whether the hrpE gene is responsible for the formation of the Hrp pilus. In this study, the hrpE gene was knocked out and found that the hrpE mutant lost pathogenicity in rice and the ability to trigger HR(hypersensitive response) in tobacco. The mutant did not interact with rice cells and its growth was reduced in rice tissues, compared to the wild-type of the bacterium. Electron microscopy revealed that the loss of pathogenicity of the hrpE mutant in rice was due to the lack of Hrp pilus formed in rice parenchyma. The complement with the hrpE gene in the mutant restored HR induction in tobacco, pathogenicity in rice and formation of Hrp pilus between bacterial and rice cells in parenchyma. It was suggested that the hrpE gene was essential for formation of the Hrppilus through which T3SS effectors were secreted into rice cells.